Conventionally, as a foundation related to the present invention, a foundation structure of a structure that includes a lower foundation built on the ground and an upper foundation built above the lower foundation with a base isolating device interposed therebetween has been known (for example, see Patent Literature 1). In this foundation structure, the upper foundation is built by casting concrete in a steel plate form that is constituted by a bottom steel plate and a side steel plate. In this foundation structure of a structure, because assembling and disassembling operations as in a concrete form can be omitted, a significant reduction in power at the time of on-site construction and a significant reduction in the construction period can be achieved.